The conclusion being reached by ever more cities is clear: diesel has to go. An increasing number of sustainable alternatives are available to transport, including public transport; most of them battery-based, some involving hydrogen. But as yet none of them offers a solution for heavy commercial transport, mainly for reasons relating to the energy density, Noud Maes explains. A few weeks ago he gained his doctorate cum laude for his detailed mapping of the combustion spray. This mist comes from the injector - in the automotive sector often called the fuel atomizer - which injects fuel under high pressure into the cylinder, thus providing an optimal combustion process.

“If you compare the amount of energy delivered by a battery weighing a kilo and a kilo of diesel, diesel wins by a factor of forty. For short journeys this is not so important and we welcome the use of electric vehicles, but where long distances are involved, every additional kilo you have to transport counts. The use of hydrogen also has its own drawbacks. The main problem is storage and, of course, it is a relatively hazardous fuel. So we are going to have to accept that where transport logistics are concerned we will remain dependent on liquid fuels in the coming decades,” says Maes.

Scope for greening

In view of this, Maes doesn't feel the negative image diesel has earned in recent years is entirely warranted. “Rare raw materials and a great deal of energy are consumed in the battery production process. All in all it is highly debatable whether electric-powered driving is that much more sustainable than diesel. We do indeed have a energy problem and must manage the energy sources we have smartly, but make this a reason to select the right energy source for each application. And don't impose a blanket exclusion on liquid fuels; as we show with our research, these too offer plenty of scope for becoming greener.”

Maes studied which steps are involved in the transition from combustion spray to heat output and recorded this in detail in order to understand exactly what happens, what influences the processes and, chiefly: how it can be done more efficiently. Because, as he explains, whereas much had already been described regarding sprays used in passenger cars, this was not the case for those in heavier truck engines. “Yet studying this at a fundamental level is precisely what is important. For example, we are seeing that we can reduce the emission of harmful combustion products by paying greater attention to flame-wall interaction.”

The experiments he performed are pretty much unique and can only be carried out in a couple of labs worldwide. Collaboration  - Maes spent a couple of months in the United States and France - has given rise to a measurement facility with international validation.

“While measurements are being taken, the pressure rises to 110 bar, the temperature to around 600 degrees Celsius. Added to which, you want to be able to see what is happening in the engine and you want to be able to create the conditions with a high degree of accuracy. That makes a set-up like this very costly and puts it beyond the reach of many labs. The data from our experiments has since been used to validate various computer simulations, so that everyone can predict sprays with great accuracy. The engines of the future will be designed based on these simulations. Various manufacturers, among them FIAT - who also sponsored our research - have already expressed an interest.”

Artwork

While his research has gained plenty of attention in its field, is widely applicable and promising - he gained his doctorate cum laude no less - personally he remains level-headed about it. Something he does feel is special, however, is the front cover of his thesis. It was designed by his mother, a visual artist. This was her first time working on a science subject. “It was an enjoyable synergy, I feel honored to use her work and her artwork will now be seen worldwide.” In a couple of weeks' time he will follow his books as he takes up his postdoc position in the States. In the lab where he previously worked awhile, an hour away from San Francisco. And as well as combustion engines, he hopes to finally have the chance to see a surfboard up close.